1. Field of the Invention
This invention relates to a fuel injector for a compression ignition engine (hereinafter referred to as a "diesel engine").
2. Description of the Prior Arts
In the conventional jerk or unit injector type injection device, a plunger is lifted by a rotating cam to compress and discharge fuel which is injected through a nozzle into a combustion chamber of the engine. The pressure and rate of injection are necessarily low at low engine speeds and high at a high engine speed so that the performance and thermal efficiency of the engine is reduced at the low speed.
To improve combustion efficiency, shorten the fuel injection period and enhance the isochoric degree with a view to further improving the thermal efficiency over the full range of engine speed and load, it is necessary to increase the injection pressure and rate. This is, however, difficult to achieve with prior art injection devices.
With the object of solving this problem, accumulating type fuel injecting devices have been developed. Several such devices have been put into practice but none are in common use.
One reason for this is that the accumulating type fuel injecting device with no booster is simple in construction and cheap but the injection period cannot be shortened to the extent desired. Further, it is difficult to reduce the minimum injection rate to the level required in small-sized diesel engine. In addition, although booster type accumulation fuel injecting devices with electronic control are capable of injecting high-pressure fuel within a short period, these are costly and not very reliable due to their complicated construction.